[BUG] Vertex AI 413 - can't count tokens

Environment

• Platform (select one):
• [ ] Anthropic API
• [ ] AWS Bedrock
• [X] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.33
• Operating System: macOS 15.5
• Terminal: iTerm2

Bug Description

When using Claude through Vertex AI, requests intermittently fail with a 413 "prompt is too long" error.
Endpoint count-tokens:rawPredict returns a 400 error, preventing accurate token counting and causing the 413 error (assumption).

It seems that issue is with field

"cache_control": {
    "type": "ephemeral"
  }

If I try to make same call without this cache_control, I received 200 OK. And in response I can see

{
    "input_tokens": 252461
}

So that's the reason for 413.

Steps to Reproduce

1. Analyze big codebase
2. It sends request with >200k tokens and fails

Expected Behavior

Chunk it to smaller requests

Additional Context

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